Transfield Services chief executive Graeme Hunt also says impact of the federal government's Border Force Act on whistleblowers has been "grossly overstated".
An independently-operated hotline was one of three reporting channels available to people working at the centres in Nauru and Manus Island, he noted.
"I absolutely encourage all of our employees, if they see anything they are concerned about - and not just as part of our operation but anywhere else - to raise it," Mr Hunt told ABC radio on Monday.
His comments came after the United Nations special rapporteur on the human rights of migrants postponed his visit to Australia, claiming the legislation prevented detention centre workers from speaking out.
Mr Hunt rejected claims by the head of No Business in Abuse (NBIA), Shen Narayanasamy, that one asylum seeker attempted suicide every four days.
In May, Transfield Services told a Senate committee there were 253 reported incidents of "actual self harm" on Nauru in the 972 days to April 2015. Of those incidents, only 10 were classed as "critical".
"I do note that Shen said people try to kill themselves every four days," Mr Hunt said on Monday.
"That is clearly not true."
Transfield wasn't against refugee advocates' attempts to change offshore detention policy but the company had a contract with the federal government to fulfil.
"What is clearly an issue is the overall context of offshore processing," Mr Hunt said.
"I would absolutely support (activist groups) GetUp! and NBIA in the context of their right to lobby to change the offshore processing policy.
"The policy is what the policy is at this point in time and we are contracted to a federal government department to provide services."
Transfield Services has a $1.2 billion contract to run the Nauru and Manus Island detention centres.
